I agree. In my opinion there are two huge dominating factors.
First is the almost ubiquitous winner-takes-all election structure in the US, leading to the two party system. There is, bar none, no fair competition in US government at a level high enough to matter.
Second, the lack of term limits allows certain people in certain positions to perpetuate momentum. In part this happens by hand picking successors through brute-force out funding the competition (in part due to the economic disparity that others in this thread have mentioned).